Donations

Donations

I work for a charity and would like to keep track of donations linked to either contacts or accounts (organizations).

I am assuming (but am not sure) that the best way to track donations would be as closed won opportunities?
If so is there a way to view opportunities further back than 6 months-since many donors to an annual gift at the end of the year.  I would like to extend it back at least 5 years.

Any other feedback for this aspect of the process is most welcome. Or is there a better way to track cash donations to a charity?